An infectious Enteritic Diseases Study Center will be established at the University of Michigan. Incidence and etiology of disease will be determined in normal families and in hospitalized cases. The families will be randomly selected from the population of Tecumseh, Michigan. Efforts will be made to identify bacterial, viral, and parasitic agents associated with these illnesses. Serologic techniques will be used to determine infection rates on a uniform basis in the entire study population. New methods will be developed for recognition of infectious agents and for studying mechanisms of pathogenesis. The ultimate aim will be control through therapy and prophylaxis.